1. Field of the Invention
The present invention relates to a method of driving a display device, and more particularly, to a method of driving a display device for displaying halftone images in frames each divided into a plurality of subframes by using an intra-frame time-division method (subframe method) like a plasma display panel (PDP).
2. Description of the Related Art
Recently, along the trend of large-type display devices, thin-type display devices have been required, and various kinds of thin-type display devices have been provided. For example, there have been provided matrix panels for directly displaying digital signals, such as gas-discharge panels like PDPs, DMDs (Digital Micromirror Devices), EL (Electro Luminescence) display devices, fluorescent display tubes, and liquid crystal display devices. Among these thin-type display devices, gas-discharge panels (for example, PDPs) can easily employ large screens because of a simple process, have excellent display quality because of a self-light-emission type, and have a quick response speed. Because of these advantages, the gas-discharge panels are considered to be a most promising candidate for use as display devices for large-screen and direct-viewing HDTVs (High Definition Televisions).
Conventionally, an intermediate tone display method of a PDP is carried out according to an intra-frame (intra-field) time-division method (subframe (subfield) method), for example. One frame (field) consists of N subframes (subfields: light-emitting blocks) of SF1 to SFN with different weights of luminance. When the interlaced operation is carried out, one frame consists of two fields of an even number field and an odd number field. These frames are essentially equivalent to frames, and in the present specification, these fields are also referred to as frames. In the present specification, description will be made based on the assumption that one pixel consists of three sub-pixels of R (red), G (green), and B (blue). While the PDP will be taken as an example in the following explanation, the present invention is not limited to the PDP, and the present invention can be widely applied to display devices for carrying out a halftone (gradation) display using the intra-frame time-division method.
As a gradation display system for the display device like the PDP, the intra-frame time-division method is usually used. This intra-frame time-division method is characterized in that the light emission period per one TV frame of each pixel expands to a maximum one TV frame. Accordingly, when an image moves and when the viewpoint of an observer (user) of a display device traces this moving image, the light emission of this pixel expands on the retina of the observer by the pixels that move in one TV frame.
Conventionally, when a moving picture is displayed on the PDP, there has been a problem that the edge portion of the display image becomes indistinct. This is because of an afterimage effect of the observer that occurs when the viewpoint of the observer traces the moving image. This disturbance is called a moving picture counterfeit outline (color counterfeit outline), and this phenomenon occurs based on the same principle as that of the large problem of the PDP as described above.
As methods of reducing this moving picture counterfeit outline, there have been proposed a method of increasing the number of light-emitting blocks by decreasing the number of gradations, and a method of a superimposed processing for restricting the move of the weight of the light emission. These methods have been proposed in Japanese Unexamined Patent Publication (Kokai) Nos. 10-039828, 10-133623, 11-249617, 2000-105565, and 2000-163004. A method of assuming an image on retina is disclosed in detail, for example, in Japanese Unexamined Patent Publication (Kokai) No. 2000-105565 that is described later.
However, when these conventional methods are used, the indistinctness of the edge portion of the image is further emphasized. Therefore, in order to obtain a natural expression of images, it is necessary to reduce the moving picture counterfeit outline without decreasing the number of gradations.
Further, in order to realize a panel for achieving a higher-precision display, it is necessary to increase the address speed, and further, a sophisticated manufacturing technique is required as well. It is not easy to increase the resolution of the PDP based on the current techniques. Further, a high resolution brings about a reduction in the luminous efficiency due to a reduction in the sizes of discharge cells.